rain.html

<!DOCTYPE html>
<html lang="zh">
<head>
	<meta charset="UTF-8">
	<meta http-equiv="X-UA-Compatible" content="IE=edge">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<title>Document</title>
	<style>
		
		*{
			margin:  0;
			padding: 0;
		}
		
		body{
			background: #333;
		}
		
	</style>
</head>
<body>
	<script>
		
		setInterval(function() {
			var rain = document.createElement("div");
			
			rain.style.position = "fixed";
			rain.style.height = "150px";
			rain.style.width = "2px";
			rain.style.background = "#FFF";
			rain.style.filter = "blur(1px)";
			rain.style.top = "0px";
			rain.style.left = Math.random() * 1920 + "px";
			rain.style.opacity = parseInt(Math.random() * 10) / 10 + "";
			
			document.body.appendChild(rain);
			
			var timer = setInterval(function() {
				var height = parseInt(rain.style.top);
				var k = 1;
				k++;
				
				rain.style.top = height + Math.pow(k, 1.5) + "%";
				
				if (parseInt(rain.style.top) >= 100) {
					clearInterval(timer);
					rain.parentNode.removeChild(rain);
				}
			}, 4)
		}, 8)
		
	</script>
</body>
</html>